The treatment of human skin with various agents has been undertaken for many years with the goal being to keep the skin in a smooth and supple condition. Skin has the tendency to dry out when exposed to low humidity or to harsh detergent solutions for extended periods of time. From a physiological standpoint, dryness is a measure of the water content of the skin. Under normal conditions, the water content and vapor pressure of the epidermis are higher than those of the surrounding air, with consequent evaporation of water from the skin surface. Skin becomes dry because of excessive loss of water from its surface which results in loss of water from the stratum corneum. Low humidity speeds up this process, exacerbating the drying of skin.
Continuous and prolonged immersion in soap or detergent solutions can contribute to dryness of the stratum corneum. The reason for this is that the surfactant medium promotes dissolution of the skin surface and horny layer lipids, and the dissolution of the hygroscopic water-soluble components in the skin.
Also, in normal skin, the stratum corneum is shed as individual cells or as small clusters of cells. Skin problems such as dry skin, psoriasis, ichtyosis, dandruff, callus, photodamaged skin, aged skin, and sunburn can be described as disorders of keratinization in which the shedding of stratum corenum cells at the skin surface is altered relative to normal, young, healthy skin. Such alteration results in shedding of large clusters of cells leading to visible scaling of the skin, a build-up of keratinaceous material on the surface or in follicles or ducts, and a rough texture to the skin surface. These conditions can be improved by removal of the outermost keratinaceous material. In other words, by desquamation.
Acne is a condition of the human skin characterized by an excess flow of sebum, or skin oil, from the sebaceous glands located in the pilosebaceous apparatus. Sebum reaches the skin surface through the duct of the hair follicle. The presence of excessive amounts of sebum in the duct and on the skin acts to block or stagnate the continuous flow of sebum from the follicular duct, thus producing a thickening and a solidification of the sebum to form a solid plug known as a comedone. When this process occurs, hyperkeratinization of the follicular opening is stimulated, thus completely closing the duct. The usual results are papules, pustules, or cysts, often contaminated with bacteria which cause secondary infections. Acne is particularly characterized by the presence of comedones, inflammatory papules, pustules, or cysts. The effect of acne ranges from slight skin irritation and pitting to disfiguring scars.
Many topical therapeutic agents are employed in the treatment of acne to prevent the blocking of the follicular duct, to reopen the duct once it has become blocked, to act against the infecting bacteria or the thickened sebum, and to provide combinations of each of these actions. The horny outer layer of the skin, which is known as the stratum corneum, is formed of dead cells composed largely of keratin. Therapeutic agents which act to prevent the blocking of the follicular duct by promoting the removal or sloughing off of excess keratin are known as keratolytic agents. However, many anti-acne compositions are harsh and irritating to the skin.
Therefore, there is an ongoing need to effectively deliver a wide variety of active ingredients, particularly anti-acne actives, to the skin, either via direct application of such a composition, or in the case of a cleansing composition, via the cleansing process. There is a need for developing products which are gentle and nonirritating to the skin.
It has been found in the present invention that skin care compositions containing a combination of an amphoteric surfactant and an anionic surfactant, further in combination with an active ingredient, are useful for providing these skin care benefits. When the active ingredient is salicylic acid or benzoyl peroxide, these compositions have been found especially useful for treating or cleansing the skin, especially skin that is afflicted with acne. These compositions are found to provide improved anti-acne efficacy. These compositions have been found to be gentle and nonirritating and to leave the skin feeling soft and smooth.
It is therefore an object of the present invention to provide skin care compositions for topical application to the skin.
It is another object of the present invention to provide skin care compositions which are useful for efficiently delivering a wide variety of active ingredients to the skin.
It is another object of the present invention to provide skin care compositions having improved skin conditioning and dryness reducing properties.
It is another object of the present invention to provide compositions which are useful for treating and preventing acne, while being mild and nonirritating to the skin.
It is another object of the present invention to provide skin care compositions which, when in the form of cleansing compositions, are useful for delivering a wide variety of active ingredients to the skin via the cleansing process.
It is another object of the present invention to provide methods for treating the skin.
It is another object of the present invention to provide methods for delivering active ingredients to the skin, to provide methods for treating acne, to provide methods for treating dry skin, to provide methods for cleansing the skin, to provide methods for reducing pore size, to provide methods for clarifying the skin, and to provide methods for desquamating the skin.
These and other objects will become readily apparent from the detailed description which follows.